sorry to reply like that, wasn't being insultive, its just that writing zeroes will still cause data to be recovered. The killdisk runs by alternatley writing 1 then 0 in pattern that way the information is completely discernable. not trying to be an a$$ or anything, honest
Anyhow, there is still a slight charge on a zero that was once a one and it can be recovered by special means. Zero and full format are fairly similar. To remove completely you need a program that alternatley writes info and essentially it will scramble the drive. After that it will then do multiple passes of writing zeros. It will, however, do the pattern first so that even if FBI or whoever gets it the residual data will be just a pattern of garbage due to the program.
Here's a nifty little sight just found so editing this real quick. Wow, this guy goes REAL indepth, but it'll tell you how its done and recovery procedures done and the preventions and random writes to make it unreadable to destroy secure data: